Method of applying a protective coating over a photographic print



June 19, 1956 H c. STAEHLE 2,751,315

METHOD OF APPLYING A PROTECTIVE COATING OVER A PHOTOGRAPHIC PRINT Filed Jan. 2, 1953 PHOTOGRAPH/C PRINT I Fig.1

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ATTORNEYG AGE/VT United States Patent METHOD OF APPLYING A PROTECTIVE COATING OVER A PHOTOGRAPHIC PRINT Henry C. Staehle, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application January 2, 1953, Serial No. 329,227 9 Claims. (Cl. 117--76) This invention relates to a process for applying synthetic polymer layers to the surface of processed photographic elements.

It is well known that photographic elements such as prints, negatives, positive transparencies, etc., both black and-white and colored, and especially those containing gelatin emulsion layers, are readily soiled in handling, particularly through finger-prints which are not readily removable. Such elements are also quite susceptible to abrasion, dust contamination, fungus, and other biological attack, and may undergo undesirable decomposition under adverse conditions of temperature and humidity. A limited amount of success has resulted from coating the viewing surfaces of such elements with protective layers from which the undesirable markings are more readily removable and which protect the elements from atmospheric effects.

Also, it is a common practice in photography to pro vide paper prints with various surfaces or textures such as glossy, semi-matte, matte, etc. In the latter two cases, the most common procedure is to provide the baryta coating for the photographic element with the desired surface characteristics which are manifest in the final print upon air drying. Surfaces of highest gloss are obtained primarily by ferrotyping the print, generally by drying the print with the emulsion surface in contact with a polished metal surface.

One object of my invention is to provide a method of coating photographic images with protective layers and simultaneously to impart the desired surface characteristics to the elements.

in general, the objects of my invention are accomplished by squeegeeing the emulsion layer of a processed photographic emulsion onto a moisture-repellent surface which may have been waxed, with a thin film or layer of an aqueous colloidal dispersion of certain polymers between the moisture-repellent surface and the emulsion layer. Thereafter, the emulsion layer and polymer are detached from the moisture-repellent surface with the result that a transparent layer of the polymer remains on the emulsion surface. When it is desired to obtain a glossy surface layer in this manner, the moisture-repellent surface used can be that of a highly polished metal plate or other material substantially impermeable to moisture. When surfaces having other light reflection properties are desired, one selects for the surfacing element a suitably textured surface such as an embossed metal plate. In this manner the prints can have a variety of surfaces such as tapestry, silk, matte, semi-matte, etc. One advantage of the latter procedure is that it is not necessary to depend upon a subcoating for the emulsion layer, such as a baryta coating, for obtaining the desired emulsion surface characteristics. Accordingly, more uniformity of product is obtainable by my process.

The aqueous colloidal dispersions of polymeric materials suitable for applying the surface layers to processed photographic elements are somewhat limited. As is well 2,751,315 Patented June 1 9, 1956 known, many monomeric materials can be polymerized in aqueous medium to obtain colloidal dispersions in water. Not all of such colloidal dispersions are useful in my invention. For example, dispersions of only poly-- n-butyl acrylate, polyethyl acrylate, copolymers of methyl acrylate and ethyl acrylate (SO/50), butadiene' styrene (/25), butadiene-styrene (45/55), when used in the manner of my invention, yield elements of the surfaces of which are too sticky to be of any practical value. Other dispersions such as of the ethyl acrylateacrylonitrile copolymer (SO/50) yield powdery coatings rather than continuous adherent coatings on emulsion layers when employed in the manner of my invention. Similarly, dispersions of polyvinyl ethers and polyacrylic acid methyl ester either yield sticky or powdery coatings.

The aqueous polymer dispersions useful in my invention are those of copolymers of methyl, ethyl, propyl and butyl acrylates such as n-butyl acrylate and isopropyl acrylate, with at least one monomer of the group: styrene, acrylonitrile, methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, and N-isopropyl acrylamide.

Aqueous dispersions of copolymers of the following components are particularly useful in my invention:

1. 4% ammonium acrylate 67% n-butyl acrylate 29% styrene 2. 4% ammonium acrylate 67% n-butyl acrylate 29% acrylonitrile 3. 23% N-isopropyl acrylamide 63% n-butyl acrylate 14% acrylonitrile 4. 16% N-methyl methacrylamide 59% n-butyl acrylate 25% styrene 5. 50% n-butyl acrylate 50% acrylonitrile 6. 59% isobutyl acrylate 16% methacrylamide 25% styrene 7. 84% n-butyl acrylate 16% methacrylamide 8. 59% n-butyl acrylate 16% methacrylamide 25% styrene 9. 4% N-methyl methacrylamide 48% n-butyl acrylate 48% acrylonitrile 8% N-methyl methacrylamide 46% n-butyl acrylate 46% acrylonitrile 8% -methyl methacrylamide 36.8 n-butyl acrylate 55.2% acrylonitrile 12% N-methyl methacrylamide 44% n-butyl acrylate 44% acrylonitrile The dispersions of copolymers such as dispersions 1, 2, 4 and 6 to 12 can be obtained as described in the Fowler U. S. Patent application Serial No. 272,709, filed February 20, 1952, and may contain solid concentrations of the order of 20 percent or more as desired.

'Dispersions such as 3 and 5 above which yield substantially hydrophobic coatings when applied to photographic elements in the manner described, are prepared N,N dimethyl N ,8 hydroxylethyl ammonium chloride, sodium lauryl sulfonate, di-Z-ethylhexyl sodium sulfosuccinate etc. Dispersions such as 6 to 8 are less moisture-repellent due to their methaeryl Cop olymers; 9-,-l2 above are representative. of a group ofpopolymers forming a preferred embodiment-of my inyention. Thisgroup of copolymers contain from about 1 to25,% by weight of the combined monomers, N- methy-l methacrylamide or N-ethyl methacrylamide, fromabout 2574% by weight of a combined lower alkyl acrylate such as n-butyl acrylate, and from about 25 to 74% by weight of combined acrylonitrile. When these copolymers are used in the process of my invention, .for coating processed gelatin emulsion layers, the resultantcoatings have the combination of desired properties: good adherence to the emulsion, low water-permeability, good flexibility, and relatively high melting point. The ,latter characteristic is of particular importance. when the coated prints are to be subjected to elevated temperatures in contact with each other or an absorptive surface as in a dry mounting press, and when it is thus desirable to prevent the emulsion overcoating frornmelting and adhering to such surfaces.

As is apparent from the above, the acrylamide component of the copolymers can be varied to control the hardness and adhesion of the polymer coatings to the emulsion surface; the alkyl acrylate component controls flexibility and moisture permeability as does the acrylonitrile component.

The method I use for applying the polymeric compositions to the processed photographic elements is i1- lustrated in the accompanying drawings wherein Fig. l shows in greatly enlarged cross-sectional view the pro cedure of squeegeeing a print to a surface element, with a bead of the copolymer dispersion between the two elements. Fig. 2 shows the laminated assembly after squeegeeing and Fig. 3 the detachment of the glazed print from the glazing or surfacing element.

My process will now be described with particular reference to the accompanying drawings. As shown in Fig. l of the drawings, a plate 10 such as polished or textured aluminum, chromium, or. synthetic resin is provided. This plate may be waxed, for example, with an extremely thin coating of carnauba wax, beeswax, or parafiin, etc., and polished if desired. In some cases it will be found that litle or no waxis required particularly when using metal plates. A pool or bead of the aqueous colloidal dispersion of copolymer 11 is then applied at one edge of the plate 10 and the processed photographic element such as a paper print which has been devel- I oped and fixed as usual, including a support 12 and gelatin emulsion layer 13 containing theimage 14 is then squeegeed on to the plateby means of rollers 15.- Fig. 2 shows the appearance of the laminated element after this procedure according to which the copolymer layer 16 is shown as having lost mostof its moisture content due to the absorption of the water ofthe dispersion by the adjacent gelatin emulsion layer 13.-

Fig. 3 shows the print being detached from the plate 10, leaving a substantially dry, uniform coating of the copolymer 16 attached to the emulsion layer 13. Since this procedure utilized plate 10, the surface of which is highly polished, water-impermeable and non-adherent tolayer 16, when the print carrying the copolymer coatingis viewed, it is found to have a surface as glossy as obtainable bylconventional ferrotyping methods.

Toluolf 4 The organic solvents are absorbed by the latices by milling the composition overnight.

As mentioned, the ethyl acrylate-acrylonitrile dispersion, if used alone, dries to a fine, white powder. The organic solvents in the above composition, together with the other copolymer, induce the formation of a homogeneous, clear film upon drying. The latter copolymer also improves adhesion of the coatings .to .the gelatin surfaces of the photographic elements.

It will be apparent thatrny process, is not limited to..

applying the copolymer coatings to dry photographic elements since it is equally useful with freshly processed elements still damp with processing solutions or wash water. Naturally, excess watertshould be removed from the photographic element prior tothe lamination step to prevent undue dilution of the copolymer dispersions.

My process is especially useful in applying protective coatings to photographic elements containing colored images in gelatin layers.

such as by color development of gelatino-silver halide emulsion layers in the presence of coupler compounds,

or by imbibition dye printing methods in which dye images are imbibed onto gelatin layers, etc. In the mannerdescribed above, the color prints or films are squeegeed to the surfacing element, utilizing the copolymer vdispersions, and separation of the temporarily laminated-ele-. ment yields a photographic element carrying a coating of copolymer on the colored image, of the desired sur face texture. In this connection, the surface coating on. colored photographic elements may serve a further purpose if an ultra-violet absorber is incorporated into the The absorber prevents harmful ultra-violet rays from reaching the colored images and copolymer dispersion.

thereby increases the stability of the colored images. However, a preferred method includes first applying the ultra-violet absorber to the emulsion surface of the element and then applying the protective coating of polymer in the manner described above. For example, a solution of 1 gram of an absorber such as 2-phenylirn-.

glazing operation described above can then be employed I to provide the color print with a protective coating.

My process is especially applicable to protecting photographic elements prone to deterioration in the presence of heat and moisture. and films which have been stabilized so as to obviate the washing step following fixing, for example, asdescribed in the Russell U. S. Patents 2,453,346 and,

2,453,347, and BriceU S. Patent 2,448,857 are coated as described above with layers of the more moisture-re pellent copolymer dispersions to obtain moisture-impermeable coatings over-the emulsionlayer with the result that moisture is materially prevented from deteriorating the silver images. When such stabilized photographic elements also include a moisture-impermeable support, moisture is entirely prevented from reachingthe emulsion layer containing the stabilizedzsilver image.

My process is readily adaptedto the continuous production of elements carrying a coating of the copolymer}- compositions. A procedure is now available by which;

black-and-white or colored motion-picture elements are continuously laminated to the desired surfacing element by means of a bead of copolymer dispersion and continuously strippedfromthe surfacing element to obtain, a layer of thecopolymer attached to the emulsion layer containing the photographic image- Similarly, paper,

tilt n and other websfireeofphotographic imagescan be.

quiet y; qa dtb i xpmqe st- I e elr pp rt Such elements containing colored images are obtainable by well known methods.

For example, silver paper prints polymer dispersions to the web, or to the surfacing element, by the usual coating methods and thereafter laminate the web to the surfacing element by means of rollers and then strip the two elements apart as descn'bed above. In such application it is desirable to use an endless belt of suitable material as the surfacing element, as will be readily understood. Obviously, this procedure possesses the advantage that extensive drying methods are obviated inasmuch as a minimum of coplymer dispersion is used.

What I claim is:

1. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, which comprises squeegeeing said emulsion layer onto a water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing from about 1 to 25% of combined N-methyl methacrylamide, about 25 to 74% of combined n-butyl acrylate, and about 25 to 75% of combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

2. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, which comprises squeegeeing said emulsion layer onto a water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing from about 4 to 12% of combined N-methyl methacrylamide, about 44 to 48% of combined n-butyl acrylate and about 44 to 48% of combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

3. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, Which comprises squeegeeing said emulsion layer onto a water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing about 4% combined N-methyl methacrylamide, about 48% combined n-butyl acrylate, and about 48% combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

4. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, which comprises squeegeeing said emulsion layer onto a water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing about 8% combined N-methyl methacrylamide, about 46% combined n-butyl acrylate, and about 46% combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

5. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, which comprises squeegeeing said emulsion layer onto a water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing about 8% combined N-methyl methacrylamide, about 36.8% combined n-butyl acrylate and about 55.2% combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

6. A method of applying a protective coating over a supported processed gelatin emulsion layer containing a photographic image, which comprises squeegeeing said emulsion layer onto a Water-repellent surface with a layer between said emulsion and said surface, of an aqueous colloidal dispersion of a copolymer containing about 12% combined N-methyl methacrylamide, about 44% combined n-butyl acrylate, and about 44% combined acrylonitrile, thereafter removing said emulsion and copolymer layers together from said surface to obtain a coating of the copolymer on the emulsion surface.

7. The process of claim 1 in which the photographic image is colored.

8. The process of claim 1 in image is black-and-white.

9. The process of claim 1 surface is embossed.

which the photographic in which the water-repellent References Cited in the file of this patent UNITED STATES PATENTS 31,906 Rawson Apr. 2, 1861 2,123,599 Fikentscher July 12, 1938 2,140,048 Fikentscher Dec. 13, 1938 2,173,480 Jung Sept. 19, 1939 2,267,470 Kabela Dec. 23, 1941 2,311,518 Caligari Feb. 16, 1943 2,550,652 Drechsel Apr. 24, 1951 2,592,218 Weisgerber Apr. 8, 1952 OTHER REFERENCES Ser. No. 397,138, Fikentscher (A. P- C-), Published May 11, 1943. 

1. A METHOD OF APPLYING A PROTECTIVE COATING OVER A SUPPORTED PROCESS GELATIN EMULSION LAYER CONTAINING A PHOTOGRAPHIC IMAGE, WHICH COMPRISES SQUEGEEING SAID EMULSION LAYER ONTO A WATER-REPELLENT SURFACE WITH A LAYER BETWEEN SAID EMULSION AND SAID SURFACE, OF AN AQUEOUS COLLOIDAL DISPERSION OF A COPOLYMER CONTAINING FROM ABOUT 1 TO 25% OF COMBINED N-METHYL METHACRYLAMIDE, ABOUT 25 TO 74% OF COMBINED N-BUTYL ACRYLATE, AND ABOUT 25 TO 75% OF COMBINED ACRYLONITRILE, THEREAFTER REMOVING SAID EMULSION AND COPOLYMER LAYERS TOGETHER FROM SAID SURFACE TO OBTAIN A COATING OF THE COPOLYMER ON THE EMULSION SURFACE. 